Supposedly the same molecules but different masses, radioactivity (Radio-09) The reaction of bromine with hydrogen produces hydrogen bromide gas (HBr). The following isotopes are involved in the reaction: 1H, 2H, 79Br and 81Br. What is the balanced reaction equation? How many different HBr molecules with different masses are formed? Which isotope combination would be the lightest HBr, which is the heaviest HBr molecule? Indication including molar mass Assumptions for the molar masses: it is calculated by simplifying that m(Proton) = m(Neutron). the following shall apply: M(1H) = 1 g/mol, M(2H) = 2 g/mol, M(79Br) = 79 g/mol and M(81Br) = 81 g/mol.

  Exercise: Radio-09    

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The reaction of bromine with hydrogen produces hydrogen bromide gas (HBr). The following isotopes are involved in the reaction: ¹H, ²H, ⁷⁹Br and ⁸¹Br.

1. What is the balanced reaction equation?
2. How many different HBr molecules with different masses are formed?
3. Which isotope combination would be the lightest HBr, which is the heaviest HBr molecule? Indication including molar mass

Assumptions for the molar masses: it is calculated by simplifying that m(Proton) = m(Neutron). the following shall apply:
M(¹H) = 1 g/mol, M(²H) = 2 g/mol, M(⁷⁹Br) = 79 g/mol and M(⁸¹Br) = 81 g/mol.

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Solution:

1. H₂ + Br₂ ⇄ 2 · HBr
2. There is 4 different possible pairs:
       ¹H-⁷⁹Br, ¹H-⁸¹Br, ²H-⁷⁹Br and ²H-⁸¹Br
3. M(¹H-⁷⁹Br) = 80 g/mol, M(¹H-⁸¹Br) = 82 g/mol, M(²H-⁷⁹Br) = 81 g/mol, M(²H-⁸¹Br) = 83 g/mol
       Light molecule ¹H-⁷⁹Br, heaviest molecule ²H-⁸¹Br

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